The present disclosure relates to a dimple processing method for forming dimples on the surface of a workpiece by using a rotary cutting tool to make small recesses on the surface.
A plurality of dimples in the form of small recesses may be formed on the surface of a workpiece that may be made of aluminum, copper alloy, casted product thereof, cast iron, resin, or the like. The plurality of dimples may form, as an example, a satin finish on the surface of the workpiece. The dimples may be formed on the workpiece to reduce the frictional resistance between the workpiece and a counter piece in contact with the workpiece. The principle is described as follows: when the workpiece comes in contact with the counter piece, abrasion powders are generated between the workpiece and the counter piece, and increase the frictional resistance. With dimples are formed as recesses on the surface of the workpiece, the abrasion powders may be retained in the dimples, thereby limiting the increase in frictional resistance caused by the generation of the abrasion powders. Dimples may also be employed when oil is poured between the workpiece and the counter piece so that oil can fill and gather in the dimples. In this case, when the counter piece passes near the dimples, the oil is discharged from the dimples and enters into the space between the counter piece and the workpiece, due to a high pressure squeezing effect. This pressure may prevent the counter piece from coming into contact with the workpiece, thereby reducing the frictional resistance between the counter piece and the workpiece.
Dimples may be formed on an inner wall of a cylinder for an engine, or an inner wall of a tubular member for a turbocharger etc., or a joining face of an artificial joint or the like. Methods for processing dimples such as a method using laser irradiation, as well as a method using shot peening in which microbeads collide with a workpiece at high speed are known in the art. When using the laser irradiation method, the workpiece is heated at a high temperature, which may apply of a large amount of thermal stress to the workpiece, or dross (molten material) adhering to the workpiece. It may be difficult to remove any bulging portions or dross portions that are formed by the laser. When adopting the shot peening method, the area around dimples may bulge so that the workpiece may not be flat. In addition, residual stress may be generated around the dimples and may cause deformation or breakage of the workpiece.
Japanese Laid-Open Patent Publication No. 10-052998 discloses a method for decorating a surface of a workpiece using a rotary cutting tool, such as a milling cutter, end mill cutter, or the like. In this method, the cutting edge of a rotary cutting tool is brought into contact slightly with the surface of the workpiece, while rotating the rotary cutting tool. In this way, for example, a polka-dot pattern with a plurality of circles can be formed on the surface of the workpiece. The circles are arranged parallel to the longitudinal axial direction of the rotary cutting tool and are formed at equal intervals in the feed direction orthogonal to the axial direction.
There has conventionally been a need for reducing frictional resistance more uniformly through the use of dimples. For this need, for example, a processing method, that easily allows the formation of a plurality of very small dimples, is desired. Further, there has also been a need to prevent burrs from being built around the dimples, and to maintain the area surrounding the dimples as flat. Therefore, a method for processing a plurality of, for example, very small dimples by a rotary cutting tool has been conventionally needed.